Metal is formed by a variety of methods, typical examples of which include mold casting and forging. Casting and forging are suitable for mass production since metal can be rapidly and accurately formed thereby.
A mold device for casting or forging has a cavity, a space in which a product is formed, formed by a movable mold and a fixed mold assembled together. After metal is melted by heating, the resulting molten metal is injected into the cavity to fill the cavity (casting) or is solidified by pressurizing the molten metal (forging). Afterwards, the movable mold is separated from the fixed mold, and a formed product is subsequently taken out.
In this case, the formed product is taken out by removing the formed product from the movable mold using ejector pins. When the movable mold is separated from the fixed mold, the formed product remains attached to the movable mold. Since the length of the ejector pins extends through the movable mold to the cavity, the ejector pins are moved towards the cavity by a cylinder to push against the formed product, thereby detaching the formed product from the movable mold.
In the process of forming molten metal, the molten metal rapidly oxides through contact with air, and this also allows introduction of impurities into the molten metal, thereby forming dross. Although the dross reduces the contact of the molten metal with the air, the dross impedes continuous stirring during melting of the metal, thereby reducing the high-quality of the molten metal. In order to overcome this problem, mold devices for forming metal in a vacuum environment have been proposed.
However, in mold devices that use ejector pins to eject out a formed metal product, it is difficult to create a high-level vacuum environment because of small gaps between the ejector pins and the hole through which the ejector pin extends. These small gaps can allow atmospheric air to enter the mold cavity.